Improvements in particle production technologies have recently been accompanied by advances in the attempt to enhance the functions of particles. Therefore, there has been a demand for a technique for accurately evaluating particles in industrial fields.
Particles are employed in a variety of fields. For example, particles are used in many products that are seen in everyday life, such as battery materials, cosmetics, pharmaceutical products, rubber, resins, food additives, paint, and pigments. However, particle evaluation technology has not yet been much advanced.
For example, the surfaces of silica gel particles that are widely used as a dispersant are chemically modified in various manners. Specifically, the surfaces of the silica gel particles are modified by modifier molecules. The modifier molecules impart functions, such as hydrophobicity and the like, to the silica gel particles. The surface-modified particles are evaluated by elementary analysis by microscopic Raman spectroscopy or elementary analysis by electron microscopy. However, in these evaluation methods, it takes a very long time to complete one measurement. For example, it takes about one hour to measure a single particle.
Therefore, the elementary analysis by microscopic Raman spectroscopy or electron microscopy has not been applicable to quality control or the like in industrial fields. In industrial fields, it is necessary to analyze a large number of samples. In addition, the elementary analysis by microscopic Raman spectroscopy or electron microscope cannot be used to measure important aspects, such as surface coverage rate of modifier molecules and the like. The surface coverage rate of modifier molecules refers to the proportion of an area occupied by the modifier molecules to the surface area of a particle. Also, none of the surface area of a particle, the diameter of a pore formed in a particle, and the like, which are other aspects of a particle to be evaluated, can be measured by the elementary analysis by microscopic Raman spectroscopy or electron microscope.
The surface area of a particle and the diameter of a pore formed in a particle, are typically measured using the mercury intrusion technique or the Brunauer-Emmett-Teller (BET) technique. In the BET technique, inert gas, such as nitrogen gas or the like, is used. However, neither the mercury intrusion technique nor the BET technique can be used to measure particles in a solution. Therefore, neither the mercury intrusion technique nor the BET technique can be used to accurately determine the surface area or the like of polymer particles that swell in a solution, in a solution that is an environment where the particles are actually used. Moreover, neither the mercury intrusion technique nor the BET technique can be used to measure particles individually.
The surface coverage rate of modifier molecules can be determined on the basis of the amount of reaction of the modifier molecules. The amount of reaction of modifier molecules is estimated by comparing the amount of modifier molecules that have been used to modify the particle surfaces with the amount of modifier molecules that have remained as residue. However, the measurement method cannot be used to sufficiently evaluate variations in the surface coverage rate. Therefore, it is difficult to accurately measure the surface coverage rate.
Meanwhile, the present inventors have proposed a porosity measuring device (Patent Literature 1). The porosity measuring device is used to measure the porosities of individual particles of a dispersoid dispersed in a dispersion medium and the volumes of the void space of the individual particles of the dispersoid, using the volume magnetic susceptibility (magnetic susceptibility per unit volume). In the porosity measuring device, the dispersion medium may be liquid or gas. Also, the particle may be, for example, a fine particle or a cell.